1. Field of the Invention
This invention relates to novel polymeric peroxides derived from hydroxy-hydroperoxides and dihydroxy-dialkyl peroxides. The present invention also relates to the preparation and use of these novel polymeric peroxides for curing unsaturated polyester resins, polymerizing ethylenically unsaturated monomers, curing elastomer resins, reducing the molecular weight and modifying the molecular weight distribution of polypropylene/propylene copolymers, crosslinking olefin polymers and preparing block copolymers and for compatibilizing polymeric blends and alloys.
2. Description of Prior Art
Addition polymers, such as polystyrene (PS), poly(methyl methacrylate) (PMMA), poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVAc), polyethylene (PE) and polypropylene (PP) and condensation polymers, such as polycarbonates, polyesters, polyurethanes, polyimides and polyamides (e.g., nylons) possess highly differing physical and chemical properties. These addition and condensation polymers are also generally made by very different processes.
In general, commercial addition polymers are made by free radical, anionic or cationic chemical processes. Addition polymers are generally produced from monomers possessing ethylenically unsaturated double bonds. Furthermore, commercial addition polymers are commodity polymers, i.e., they are produced in large volumes, are easily processed in polymer processing equipment, have low unit prices and low profit margins. Free-radically initiated addition polymers generally do not have acceptable high temperature properties that would enable them to be used alone in engineering applications. Thus, addition polymers are not considered to be "engineering thermoplastics."
In contrast, commercial condensation polymers are produced by condensation chemical processes and are generally produced from one or more monomers that chain extend via classical condensation chemistry. Commercial condensation polymers are generally produced in much lower volumes, are more difficult to process, have high unit costs and are much more profitable. Owing to their high temperature properties, commercial condensation polymers, such as aromatic polycarbonates, polyarylates and nylons, are used extensively in engineering thermoplastic applications.
Peroxides are generally only used to initiate polymerization of monomers that can generally only form addition polymers. Peroxides generally cannot initiate polymerization of condensation monomers.
Resin compounders continually strive to improve the cost performance parameters of both commodity addition polymers and engineering thermoplastics by blending the commodity addition polymers with engineering thermoplastics. In rare instances, completely miscible or compatible blends are obtained when engineering thermoplastics are blended with commodity addition polymers.
In recent years, most of the new, commercialized polymeric materials are polymeric blends and alloys composed of two or more different polymers. This trend of commercially developing polymeric blends and alloys is due in part to the short time required for developing and commercializing these materials; the relatively low R&D cost involved for developing these materials as compared to the cost for developing entirely new polymers from monomers; and the ability to develop polymeric blends and alloys that are "tailor made" to meet end-use property specifications.
A non-limiting list of the polymer property improvements achieved by blending include:
(1) Better processability; PA1 (2) Impact strength enhancement; PA1 (3) Improved flame retardance; PA1 (4) Improved barrier properties; PA1 (5) Improved tensile properties; PA1 (6) Improved adhesion; PA1 (7) Improved melt flow; PA1 (8) Enhanced heat resistance; PA1 (9) Enhanced heat distortion temperature (HDT) PA1 (10) Improved stiffness: PA1 (11) Improved chemical resistance; and PA1 (12) Improved ultraviolet light stability.
The major problem encountered in developing new polymeric blends and alloys is the inherent incompatibility or immiscibility of almost all mixtures of two or more polymers. For example, almost all blends of addition polymers with condensation engineering thermoplastics are incompatible. The consequence of incompatibility of polymeric blends and alloys is that they are thermodynamically unstable and, consequently, do not have good mechanical and thermal properties. With sufficient time and temperature, the polymeric blends and alloys generally coalesce into separate phases.
An approach used by resin compounders to improve the compatibility of immiscible blends is to use a block copolymer as a compatibilizing agent for the incompatible polymer blend. Generally, the block copolymer should have polymeric segments that are compatible with both polymeric components of the blend. For example, when trying to form a stable blend of an addition polymer with a condensation engineering thermoplastic polymer, a compatible blend is more likely obtained if the block copolymer has addition polymer segments and condensation polymer segments.
Low cost polymeric blends and alloys are generally commercially produced from two or more addition polymers, such as polymeric blends comprising low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and polypropylene (PP). The compatibility of these low cost polymeric blends can be improved by crosslinking the polymeric blends with peroxides or by using compatibilizing block copolymers as mentioned above. Such compatibilizing block copolymers would generally have to be made from appropriate addition polymeric peroxides.
The most profitable polymeric blends and alloys are those made from low cost, commodity addition polymers initiated by free radicals and high cost, high value engineering condensation thermoplastic polymers. Here, the resin producer is either trying to up-grade the physical properties of the low cost commodity addition polymer or is trying to lower the cost of the engineering resin without significantly deleteriously affecting the polymer properties.
Polymeric peroxides are often used for preparing block copolymers. In general, block copolymers are useful for compatibilizing blends of polymers that are otherwise incompatible. Thus, there is a demand in the polymer industry for polymeric peroxides, since these polymeric peroxides can be used to produce block copolymers which in turn can be used as compatibilizing agents for polymeric blends and alloys derived from polymers that are incompatible with each other. The most effective compatibilizing block copolymer compositions are those which contain the greatest amount of block copolymer and the least amount of homopolymer. The polymeric peroxides of the present invention are very effective for preparing block copolymer compositions possessing lowered levels of homopolymer.
A block copolymer of two or more ethylenically unsaturated monomers can be made by partially decomposing the polymeric peroxide in the presence of a monomer, followed by decomposing the resulting polymeric product in the presence of a second monomer, and so on. These processes can be carried out in solution or in polymer processing equipment, such as an extruder.
Since block copolymers have utility in compatibilizing polymeric blends and alloys, there is a need for processes that produce block copolymer compatibilizing agents where one polymer segment is an addition polymer segment and the other polymer segment is a condensation engineering polymer segment.
In general, the polymeric peroxides of the prior art are not as effective for producing condensation-addition block copolymers as the novel polymeric peroxides of the present invention.
U.S. Pat. No. 4,304,882 discloses polymeric peroxides having peroxyester, monoperoxycarbonate, diperoxycarbonate, dialkyl peroxide and diperoxyketal moieties at the polymer chain ends and various polymeric peroxides with peroxyester and diacyl peroxides having 10 hour half-life temperatures below about 75.degree. C. as recurring moieties along the polymer backbone chain. Decomposition of the peroxide end groups results in formation of one macro-free radical and one micro-free radical. In the presence of an ethylenically unsaturated monomer, the formed macro-free radical produces a block copolymer including addition monomer polymer blocks (AMP) and the formed micro-free radical produces a homopolymer also containing AMPs, as illustrated by the following equations: ##STR3##
Thus, as illustrated by the above equations, a mixture of a block copolymer and a homopolymer is produced. This is undesirable since the presence of a homopolymer decreases the effectiveness of the block copolymer composition for compatibilizing blends of polymers, which is a major utility of block copolymers.
The polymeric peroxides disclosed in U.S. Pat. No. 4,304,882 having recurring diperoxyester functions cannot be used to prepare block copolymers that are relatively free of homopolymers. This is a result of the recurring diperoxyester functions ultimately decomposing to two macro-free radicals and one micro-diradical. Although the macro-free radicals result in formation of a block copolymer, the micro-diradical results in formation of significant amounts of a homopolymer: ##STR4##
The polymeric peroxides of U.S. Pat. No. 4,304,882 possessing diacyl peroxide recurring units can be used for preparing a block copolymer that is relatively free of homopolymer, since a diacyl peroxide recurring unit decomposes to two macro-free radicals. However, the generally low 10 hour half-life temperatures of these recurring units (i.e., below 75.degree. C.), limit the usefulness of these polymeric peroxides. Polymeric peroxides are typically used in applications at higher temperatures where the diacyl peroxide-polymers of U.S. Pat. No. 4,304,882 would prematurely decompose.
U.S. Pat. No. 4,283,512 discloses polymeric peroxide compositions having recurring diacyl peroxide units and U.S. Pat. No. 4,318,834 discloses polymeric peroxide compositions having recurring diacyl peroxide units and recurring diperoxyester units. In addition, both references disclose the use of these polymeric peroxides for initiating polymerization of a vinyl monomer, thus making vinyl polymers having recurring diacyl peroxide units or diperoxyester recurring units in the backbone. These vinyl polymers are subsequently used for preparing mixtures of block copolymers and homopolymers by means of initiating polymerization of a second vinyl monomer.
U.S. Pat. Nos. 4,321,179, 4,315,997 and 4,593,067 also disclose polymeric peroxides with recurring diacyl peroxide or diperoxyester units similar to the other prior art polymeric peroxides, and generally have the same problems and limitations as the polymeric peroxides disclosed in U.S. Pat. No. 4,304,882.
The polymeric peroxides of the present invention possess peroxide-containing recurring moieties with 10 hour half-life temperatures higher than those of the diacyl peroxide polymers of U.S. Pat. No. 4,304,882 and the other prior art references, they are significantly more effective and useful for preparing block copolymers and thus advance the art.